More Memory For Awesome Projects

The RAM has quadrupled, from 16K to 64K. While 16K is plenty for nearly all Arduino
libraries, 64K allows for more advanced applications. Icons and graphics for color
displays and audio
effects requiring delays, like reverb and chorus, will become possible on Teensy 3.1.

Flash memory has also doubled, to 256K, and provides double the memory bandwidth.

5 Volt Tolerance on Digital Inputs

Today most new chips use 3.3V signals, but many legacy products output 5 volt
digital signals. These can now be directly connected to Teensy 3.1's digital
inputs.

All digital pins are 5 volt tolerant on Teensy 3.1. However, the analog-only
pins (A10-A14), AREF, Program and Reset are 3.3V only.

Update: Color Change Jan 22, 2014

The color of Teensy 3.1 was changed from black to green on January 22, 2014.

Before Jan 22

After Jan 22

The green material has slightly higher resolution. See
this post
for details.

Teensy 3.1 has a proper analog output. You can always filter PWM, but
true analog output responds rapidly. The output is created by the
stable reference voltage, so it's doesn't vary if your power supply
voltage changes slightly.

Two Analog to Digital Converters

With analogRead(), you can measure many signals, but only 1 at a time.
Teensy 3.1 has a second ADC, so you can concurrently measure 2 analog signals.
For stereo audio or power monitoring, sampling both left and right, or
voltage and current at the same moment is very beneficial.

** RTC requires a 32.768 kHz crystal & 3V battery. See the
Time Library for details.

Pinouts

Teensy 3.1 is meant to be a drop-in replacement for Teensy 3.0. Only 1 pin has
different functionality. The reset pin was replaced by A14/DAC, which you can
use for true analog output, or as another analog input.

Teensy 3.0

Teensy 3.1

Pins 3 and 4 gained CAN bus functions.

Pins 6, 9, 15, and 20-21 can still have SPI chip select capability, but the
labels were removed to simplify the pinout card. Currently no libraries use
the native chip selects. However, a new SPIFIFO library is in development.

Teensy 3.0

Teensy 3.1

On the back side, 2 pins gained new PWM functionality and 6 pins have new
analog input capability. A second I2C port is also added.

Reset Signal

Teensy 3.0 supported both a Program signal, to reboot into bootloader mode,
and a traditional Reset signal, for a conventional reboot that restarts your
application.

The Reset signal can be found on a new test point on the bottom side of Teensy 3.1.